1. Field of the Invention
The invention relates generally to a motor spindle for machine tools.
2. Background Discussion
Spindle units comprising an internal coolant supply to the tool through the hollow shaft of the work spindle enable a high machining performance and relatively long tool lives of the tools. The critical parts of the machining tools are intensely cooled by the internally supplied coolant so that overheating of, and resulting damage to, the critical tool sections is avoided. However, the internal coolant system requires a considerable technical complexity in that it is typically connected with an extension of the dimensions of the spindle.
From the European patent publication 0 780 192 a motor spindle for machine tools is known in which an internal coolant supply is integrated in the clamping unit. On the machine side end portion of the housing the operating means for the clamping unit is provided which is formed as a cylinder/piston unit comprising a ring-cylinder-shaped piston. The rotational feedthrough for the cooling liquid is disposed in the cavity of the ring-cylinder-shaped piston, or the ring cylinder, whereby a particularly space-saving arrangement of the operating mechanism and the rotational feedthrough is achieved.
From German patent 100 27 750 B a motor spindle for a machine tool is known which contains a work spindle or spindle shaft supported in a spindle housing in at least two axially spaced bearings. The spindle shaft is part of a modular unit insertable into the spindle housing for exchange. In addition to the front spindle bearings a further support bearing by which the spindle shaft is rotatably supported on the spindle housing and which comprises an own biasing unit is provided in the housing side section of the spindle shaft to increase the stability of the spindle shaft.
Further, a motor spindle is known from German patent publication 195 32 976 A in which the work spindle is supported in two axially spaced pairs of roller bearings and carries the rotor of the electric drive motor on its freely projecting rear end portion. In this motor spindle also an assembly formed by the work spindle, the roller bearing arrangements, and the rotor can be mounted in and removed from a housing assembly toward the front side after screw connections have been released. The mounting capability facilitates and simplifies the maintenance and repair of motor spindles since the inner assembly containing the more susceptible components can generally be removed in situ. In contrast, the complete spindle unit, including the secondary components, has to be removed from the machine in case the conventional procedure for carrying out maintenance, repair, and inspection procedures which regularly necessitates considerable efforts.